Neck and lower back pain from degeneration of the spinal disc joint constitutes a common and significant health and economic burden. Indeed, roughly 80% of adults will experience neck and lower back pain at some point in their lives due to intervertebral degeneration. Intervertebral disc degeneration is a product of lifelong, slow, and chronic degeneration that is synchronized with remodeling of the disc and neighboring bony structures. Musculoskeletal disorders of the spine and neck and lower back pain are the leading sources of disability in people less than 45 years of age, and lead to losses of over 90 billion dollars a year in the U.S. They are the 2nd most frequent reason to visit a physician, the 5th ranking cause of admission to the hospital, and the 3rd most common reason for surgical procedures.
Intervertebral degenerative disc disease contributes to structural weakness of the outer capsule known as the annulus, which leads to herniation or protrusion of the disc into the spinal canal or neuroforamina where it impinges on traversing and exiting nerve roots. Intervertebral degenerative disc disease is characterized by a progressive loss of proteoglycans and extracellular matrix in the nucleus pulposus, which causes loss of hydration and decreased joint mobility. The medical conditions associated with intervertebral degenerative disc disease include disc herniation, radiculopathy, myelopathy, spinal stenosis, and all of these are closely associated with neck and lower back pain and extremity pain from affected nerve roots.
If a patient with neck and lower back pain fails to improve with conservative management, he is often referred for a surgical intervention, of which the most common is a discectomy, with or without fusion. One alternative to discectomy is intervertebral artificial disc insertion, which is meant to provide a means of pain relief through a stable motion-sparing reconstruction of the intervertebral segment. The drawbacks of this approach is the permanent disruption of the joint, and a high risk of chronic low grade arthritis in that joint secondary to the natural biologic response of healthy or normal tissue to tissue damage.
Another approach is a biological approach, in which non-disc cells, nucleus pulposus cells, or tissue engineered disc material is inserted into the damaged NP to regenerate the matrix and restore the disc's biomechanical function. However, non-disc cells do not have the appropriate gene program required to survive in the harsh metabolic environment of the disc space, or produce the appropriate proteoglycan products, or have the intracellular biomechanical cytoskeleton and protein machinery to withstand the constant and significant compressive forces of the disc. Additionally, nucleus pulposus cells lack the ability to divide more than a few times, and thus are not a sustainable cell source for long term regeneration. Finally, to date, a viable source of tissue engineered disc material does not exist.
Tissue engineering approaches have not been successful to date, in part due to limitations in knowledge and tissue biology relative to needs of disc tissue engineering and in part, to the harsh biomechanical and biologic environment of the disc, which is inhospitable to most cell types. Finally, in the absence of a disc tissue stem cell for tissue engineering, the use of other stem cell types such as mesenchymal stem cells and embryonic stem cells has been attempted, but they do not naturally reprogram to functional disc cells successfully.
One branch of biologics uses stem cells such as mesenchymal stem cells, embryonic stem cells, and adipose stem cells in tissue engineering. One of the major obstacles in disc repair using stem cell therapy is the ability to differentiate primary stem cell explants into the appropriate cell type and/or expand them in sufficient amounts for in vivo therapeutics. Very often, the process of reprogramming or “pushing” a stem cell towards a given fate produces cells that may have some of the properties of the targeted cell type, but are not adequately functional, or a cell population extremely limited in its ability to proliferate further once they are manipulated in vitro. The stem cells thus obtained are not a viable product, because (a) they are too few; and (b) they lack the proper phenotype and/or function. Therefore, there is an urgent need in the art for a technique that provides stem cells that may be further expanded even after in vitro manipulation and maintain the proper phenotype and function. The present application answers this need.